1. Field of the Invention
A method used in a wireless communication system and related communication device are provided, and more particularly to, a method of managing multimedia broadcast multicast service (MBMS) reception in a wireless communication system and related device.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs).
Over past few years, a multimedia broadcast multicast service (MBMS) has been introduced in LTE specification. MBMS gives the opportunity to broadcast TV, film, information such as free overnight transmission of newspaper in digital form and other media in these networks. The broadcast capability enables to reach unlimited number of users with constant network load. Further, it also enables the possibility to broadcast information simultaneously to many cellular subscribers.
Two important scenarios have identified for MBMS. One is single-cell broadcast, and the second is MBMS Single frequency network (MBSFN). MBSFN is envisaged for delivering services such as Mobile TV, using the LTE infrastructure. In MBSFN the transmission happens from a time-synchronized set of eNBs, using the same resource block. The MBSFN transmission takes place on dedicated subframes referred to as MBSFN subframes, which would be used for other purpose than MBMS. For example, the UE reads a physical downlink control channel (PDCCH) grant on the MBSFN subframes for possible uplink scheduling. Namely, the MBSFN subframes may be used for non-MBMS transmission when the MBSFN subframes are not allocated for MBMS data.
In order to support the UE to receive MBMS data, the eNB provides the UE with information about which MBSFN subframes are used for MBMS control channel (MCCH), which MBSFN subframes are used for Multicast traffic channel (MTCH) and which MBSFN subframes are used for dynamic scheduling information. In addition, the eNB provides resource allocations (e.g. modulation and coding schemes (MCSs) and frequencies) for MCCH, MTCH and dynamic scheduling information in broadcast message, for example, system information.
However, when the UE subscribing the MBMS service receives a downlink assignment (DL) indicating the MBSFN subframe on PDCCH, for example dynamic scheduling or persistent scheduling, i.e. SPS, the specification does not specify how the UE should decode the MBSFN subframe. Decoding the MBSFN subframe with information/allocation not matching with what the eNB uses for encoding the MBSFN subframe causes decoding errors.
Apart from that, in the LTE system, a discontinuity reception (DRX) function has been introduced. The DRX function allows the UE to enter a standby mode during off durations (i.e. opportunity for DRX) of DRX cycles and during the off durations, stopping monitoring the PDCCH, so as to reduce power consumption of the UE. However, the MBSFN subframe may be allocated within the off durations. In this situation, the UE is unable to receive any data of the MBSFN subframe. As a result, the MBMS service is interrupted.